WHY DO WOMEN STILL lag behind men in science and math? Not because they have less aptitude, as dated stereotypes suggest. Rather, studies show that young girls tend to be steered elsewhere by social and educational forces that shake their confidence.

Somehow, Lisa Randall never got that memo.

"I was always good at math, but I was good at everything," says Randall, a professor at Harvard University who is widely regarded as the nation's pre-eminent theoretical physicist — which means she's an ace in an über-wonky branch of science that uses math to unlock the mysteries of nature. "It sounds obnoxious, but I was just smart. In school, it's kind of obvious when you're learning things faster than other kids."

She discovered physics early on, while a student at Manhattan's elite Stuyvesant High School. "It definitely seemed an odd career path," acknowledges Randall, who grew up in a middle-class family in Queens, the daughter of a salesman and a teacher. "But I liked the idea of doing something that applied to the world, not just doing abstract problems. I liked the idea that you're solving a problem that hasn't been solved before."

Randall, who earned her undergraduate degree at Harvard in just three years, has always been exceptional. She was the first female theoretical physicist to receive tenure at MIT and Harvard, and in 2007, she earned a spot alongside Tina Fey and Warren Buffett as one of Time magazine's most influential people in the world. But Randall insists she never set out to crack any glass ceilings. "I just don't think in those terms," she says. "The fact that I was first meant there was no one before me — but it wasn't an active thing I was doing."

A gifted teacher, Randall, 49, is so articulate at dissecting physics' most brain-bruising concepts — from the nature of minute subatomic particles to the vast reaches of cosmology — that she's become a regular on TV talk shows ranging from Charlie Rose to The Colbert Report. "We so much want science to say, 'This is the way it works,' that we lose sight of the fact that this uncertainty is actually interesting," she told Jon Stewart during an appearance on The Daily Show last October. (She was there to plug Knocking on Heaven's Door: How Physics and Scientific Thinking Illuminate the Universe and the Modern World, her third book.) "My hope is that if people learn more about physics and are aware of it, then they won't be so afraid of it."

While Randall's appealing TV persona and Jodie Foster-ish good looks haven't hurt her publicity efforts — last summer she was named one of the hottest female professors in the country by a college webzine — she's still an anomaly in a profession that is, without question, a boys club. (An estimated 90 percent of physics professors are male.) Randall is smart enough to know that all the publicity she generates — "When you're reaching out to people beyond the scientific community, image does matter" — helps crack the door open a little wider for other women. "If you keep telling girls they're less good at science, that will probably be self-fulfilling. But there are quite a lot of women who are good at it," she adds.

Last year, she was among only a few women to attend the prestigious Solvay Conference, an international gathering devoted to questions in physics and chemistry. "I joked on Twitter that the ratio of X to Y chromosomes at Solvay had stayed the same for the last century," Randall says, laughing. OK, so it's a joke that might not resonate with those who don't count a scientific calculator among their must-have gadgets, but name another physics professor who tweets more than 3,500 followers messages like, "Natalie Portman, first non-blonde female physicist in a movie" (referring to Thor).

Randall, who isn't married and doesn't have children, spends the bulk of her time teaching, writing, and promoting her books. Her personal life is inextricably tied to her work — for which she is unapologetic. "There are women for whom family is a priority, and they do it," she says. "It just wasn't as much a priority for me." But lest you think she's holed up alone in a windowless office somewhere, Randall also writes operas in her spare time. In 2009, she collaborated with composer Hector Parra on an opera that premiered at the Centre Pompidou in Paris, and cocurated an exhibition for the Los Angeles Arts Association called "Measure for Measure," an exploration of our perception of scale.

Still, her first love is science. "I'm happiest when I'm just doing a project," she says. "When you're actually doing physics, there are moments when things click into place and you see things you didn't see before. It's just fantastic."

LISA RANDALL'S TIPS FOR SUCCESS

1. DON'T LOOK FOR GLASS CEILINGS. In male-dominated professions, sometimes it's best to hunker down, work hard, and pay no mind to the challenges. "The fact that I was first meant there was no one before me—but it wasn't an active thing I was doing," Randall says of her accomplishments.

2. DON'T UNDERSELL YOURSELF. Too many women downplay their skills. Not Randall. "I was always good at math," she says. "But I was good at everything. It sounds obnoxious, but I was just smart."

3. LOOKING POLISHED PAYS OFF. Randall's fashion sense and good looks help sell her message: to demystify physics and get more women into the profession. "When you're reaching out to people beyond the scientific community, image does matter," she says.

Meryl Poster President of television production, The Weinstein Company

AT HER 32ND BIRTHDAY PARTY, Meryl Poster realized that her Hollywood career had really taken off. When she looked around the room at Delia's, a Manhattan supper club, she saw famous faces everywhere. "Brad Pitt and Gwyneth Paltrow were there, Sylvester Stallone, Matt Dillon, Jon Stewart, and John F. Kennedy Jr.," recalls Poster, now 47. "I guess that's when it dawned on me: I think I'm kind of successful!"

Fifteen years later, Poster is decidedly less fazed by celebrities in her midst. It's par for the course when you are the consigliere to famed movie producers Harvey and Bob Weinstein (the former hailed as "God" by Meryl Streep at this year's Golden Globes). Last year, Poster was named president of The Weinstein Company's lucrative television division, where she oversees hit shows like Project Runway and its spin-off Project Runway All Stars, along with more than 20 series in various stages of development, including a much-anticipated television adaptation of The Nanny Diaries. "When I decide I want something, I go for it. I'm totally persistent," Poster says. "My boyfriend says that if I were a superhero, I would have a big R on my chest for relentless."

The daughter of a swimsuit manufacturer, Poster grew up in Fort Lee, New Jersey, where her grandmother would sneak her out of school to take her to the movies. Watching Bedknobs and Broomsticks and Chitty Chitty Bang Bang, Poster was bitten by the fame bug. "When people would say, 'What do you want to be when you grow up?' she recalls, "I knew I wanted to walk in somewhere and have people know who I was."

She landed a gig in the legendary mail room of the William Morris Agency, famous for turning out Tinseltown rainmakers, including Michael Ovitz and David Geffen. After just three months, she was plucked from mail to work for the firm's then-president Lee Stevens, to whom she made it abundantly clear that she was no career gofer: "One day I was spilling coffee as I walked across the room, and my boss said, 'Uh-oh.' I told him, 'I don't want to get too good at this.'" Soon after, she got a call from Miramax Films, then a hot foreign- and indie-film distribution company helmed by two brash no-name brothers. Did Meryl want the job as Harvey's assistant?

At first she balked at leaving a powerful Hollywood agency for an upstart company, but ultimately she took the job, itching for a chance to carve out her own niche. "The company grew quickly. I wasn't his assistant that long," Poster explains. "I grew and took on responsibilities as the company grew. Harvey always encouraged us to take as much opportunity as we possibly could."

Poster spent 16 years at Miramax, ultimately working her way up to co-president of film production, where she oversaw the development of critical darlings like Chocolat and Chicago. The pace and responsibility were relentless—at any given moment, hundreds of people around the world would be hanging on her decisions.

She left in 2005 for a less demanding development job with NBC Universal—"I needed that time to recharge my batteries"—but returned to the Weinstein fold last year to head up their television division. "She is the ultimate," Harvey Weinstein told Marie Claire. "Meryl's taste is impeccable, and her vision is extraordinary."

Poster, divorced for five years, lives in Manhattan with her 10-year-old son and 13-year-old daughter, juggling the way all working moms do. She's taken her kids to castings, and they often tag along on her business trips to Los Angeles. "My son fell in love with Rachel Roy on the set of Project Runway," says Poster, who spends downtime taking her kids to movies and plays. That is, when she's not locking herself in the bathroom to do an uninterrupted magazine interview. "My son is outside, stalking me," she laughs.

Poster thrives on the adrenaline only a high-octane career can generate. "I'm more comfortable having power than not," she acknowledges. It also has its perks—like being an Oscar voter and getting Academy member DVDs to watch at home. "I'm always able to get a reservation at Nobu," she says. "And I still get a thrill when Robert De Niro says, 'Hi, Meryl!'"

MERYL POSTER'S TIPS FOR SUCCESS

1. BE PERSISTENT. Despite initially being turned down for a job, Poster hounded the well-known William Morris talent agency until she landed a spot in its legendary mail room. "When I decide I want something, I go for it," she says.

2. SMALLER FIRMS USUALLY OFFER MORE OPPORTUNITIES. Poster left William Morris to work as an assistant at Miramax, then an unknown movie studio. "I grew and took on responsibilities as the company grew," Poster says. "I wasn't an assistant that long."

3. KNOW WHEN IT'S TIME TO STEP BACK. After 16 years building up Miramax into a Hollywood powerhouse, Poster felt burned out and accepted a development job at NBC Universal. "I needed that time to recharge my batteries," she explains.

LAWYERS AREN'T USUALLY SUBJECT to "a star is born" moments, but Shawn Holley had hers in the early '90s while working in the Los Angeles public defender's office. She'd always liked representing the underdog and saw firsthand what fair legal representation could mean to someone in trouble. "You could make the difference between someone going to jail or being able to keep their job and provide for their family," she says. "You could keep someone's life from going into a downward spiral."

One day, Holley was in the courtroom for a complicated preliminary hearing. In the gallery: legendary attorney Johnnie Cochran. "I was feisty and fought really hard," Holley recalls. Cochran liked what he saw and poached her to work for him. Six months later, she was a part of O.J. Simpson's legal dream team, defending him against murder allegations. Though Simpson's acquittal was widely seen as a miscarriage of justice, Holley isn't troubled by it. "It's the job of the prosecution to prove someone guilty beyond a reasonable doubt—if he was guilty and got away with murder, then the prosecution failed," she says plainly.

Holley went on to head Cochran's criminal division, where she defended rappers like Tupac Shakur and Snoop Dogg. She's also represented other high-profile clients like Sara Jane Olson, the Symbionese Liberation Army bomber who evaded capture for 23 years by reinventing herself as a doctor's wife. Holley performed so effectively that she was again poached, this time by Kinsella Weitzman Iser Kump & Aldisert LLP, a boutique entertainment and business litigation firm in Santa Monica. Her practice "grew into what some people call Celebrities Behaving Badly," she says wryly.

In the years since, Holley, 50, has become the go-to attorney for stars in a fix, including indiscreet starlets like Paris Hilton, Nicole Richie, the Kardashians, and, most recently, Lindsay Lohan. Holley sees these women as underdogs—albeit famous ones—besieged by a media that delights in their missteps. "From the moment I pull up to court with Lindsay, there are cameramen jumping out of the bushes, and you can see helicopters overhead," Holley says. "You get the sense that they want to watch her go down. She's like a little girl who's in a scary place, and there are a lot of people rooting for her to fail." She's grown so attached to Lohan, in fact, that Holley says Lohan "calls me her West Coast Mom."

Surely Holley has issues securing a pass for clients so cavalier about flouting the law? "The Constitution protects us all," she explains. "It can't be a system where we pick and choose who gets a defense. I'm making sure the system is fair, and I really see that as an honorable role."

As a female partner at a law firm, Holley is a rarity. Though almost half of all law students are women, only 19 percent ever make it to partner, largely because the profession, with its emphasis on billable hours, can be ruthless to women looking to squeeze a family into the mix. Holley started hers late in life. "I always thought, One day I'll have a baby—just not right now," she admits. "By the time I was 40, I had just taken a five-year lease on a two-seat convertible and resigned myself to the fact that I wasn't going to be a mom."

And then she discovered she was pregnant. Before the year was out, she had a husband—Dorian Holley, vocalist for Jay Leno's house band—two stepdaughters, and a baby girl. As one of the few working mothers at her daughter's "fancy school," Holley has felt conflicted at times about the professional demands on her time. But her own mother had worked as a legal secretary, and Holley says she never wanted it any other way. "I admired her for going to work and getting her master's at night," she says. "I really do see the value in showing my daughters what it is to go to work and do something you think is important."

SHAWN HOLLEY'S TIPS FOR SUCCESS

1. EVERY CLIENT IS THE MOST IMPORTANT. Holley relished defending even petty-theft cases. "You could make the difference between someone going to jail or being able to provide for their family," she says of her years as a public defender.

2. DON'T APOLOGIZE FOR YOUR SUCCESS. Holley was part of O.J. Simpson's defense team. "It's the prosecution's job to prove guilt beyond a reasonable doubt—if he was guilty and got away with murder, then the prosecution failed," she says.

3. EMPATHY IS GOOD FOR BUSINESS. Holley, who has represented Lindsay Lohan and Paris Hilton, calls even her rich, sometimes reckless clients underdogs. "I'm making sure the system is fair," she says. "And I really see that as an honorable role."